The chroma value of Gac fruit powders was significantly affected
by both the drying conditions of maltodextrin level and
the inlet drying temperature. High chroma value of powders was
observed at low maltodextrin concentration and at high temperatures.
This could be due to significant interaction between the two
factors investigated. This finding is in agreement with the results
reported by Quek et al. (2007).
Lower values of a*/b* and higher hue angles were observed as a
result of increasing maltodextrin concentration and increasing the
inlet drying temperature. These results indicate that the loss of
redness of powder products increased in these spray drying conditions.
A similar result was observed by Sousa et al. (2008) who reported
that a decrease in the value of a*/b* in tomato powder was
found with increasing the inlet drying temperature. Further studies
confirmed that increased drying temperatures resulted in low
retention in the redness colour of carrot products (Chen et al.,
1995) and of tomato products (Shi et al., 1999). The possible explanation
for this phenomenon is that carrying out the spray-drying
process with a high ratio of surface area and volume of feed mixture
caused rapid pigment oxidation (Desobry et al., 1997). Therefore,
the spray drying conditions at high temperature resulted in a
high loss of red colour due to thermal degradation of carotenoid
pigment. Goula and Adamopoulos (2005) indicated that a higher
loss of lycopene content in tomato powder was observed by
increasing the air inlet temperature. In terms of the maltodextrin
concentration, moreover, the lesser redness of Gac fruit powders
was due to the higher concentration of maltodextrin used in the
spray-drying process. As previously mentioned by Grabowski
et al. (2006), increasing maltodextrin resulted in an increase in
hue angle in sweet potato powders, indicating a loss of redness.